Differential electrical connector assembly

ABSTRACT

A differential connector has a plurality of rows. Each row includes a plurality of signal conductors provided as differential pairs. Each signal conductor has a first contact end connectable to a printed circuit board, a second contact end, and an intermediate portion having a first width. For each differential pair, one first contact end lies along a first line parallel to the plurality of rows and the other first contact end lies along a second line parallel to and spaced from the first line. The differential connector further includes a plurality of ground conductors, with each ground conductor corresponding to a differential pair. Each ground conductor has a first contact end connectable to the printed circuit board, a second contact end, and an intermediate portion having a second width that is at least twice the first width.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to U.S. Provisional PatentApplication No. 60/584,928, filed Jul. 1, 2004, and U.S. ProvisionalPatent Application No. 60/638,971, filed Dec. 24, 2004.

BACKGROUND OF THE INVENTION

Modern electronic systems are typically assembled from multiple printedcircuit boards. Such printed circuit boards, which are commonly referredto as “daughter cards”, contain components thereon, such as integratedcircuits. Each daughter card also typically includes one or moreconnectors that allow the components on the daughter card to communicatewith components on the other daughter cards in the system.

One way to interconnect the daughter cards in an electronic system is toutilize a midplane. A midplane is a printed circuit board, typicallylarger than the daughter cards, to which the daughter cards areconnected—by way of connectors on both the daughter cards and themidplane—and that provides conductive paths therein. The conductivepaths, which are also referred to as “signal traces”, interconnect andprovide communication between the daughter cards in the system. Amidplane, as the name implies, provides connectors on both sides,allowing daughter cards to be connected on both sides of the midplane.The midplane can route signals between daughter cards connected on thesame side of the midplane or can cross-connect a daughter card on oneside of the midplane with a daughter card on the other side of themidplane.

In order to connect a connector to the midplane, holes areconventionally drilled through the midplane. The holes, which are alsoreferred to as “vias”, electrically connect to signal traces in themidplane. The inside walls of the vias are typically plated with aconductive material, such as metal, to provide electrical conductivity.The connector is provided with contact ends, such as press-fit contacttails or SMT (surface mount technique) contact tails, for connecting tothe vias.

As electronic systems have become smaller, faster and more complex, thishas generally required that midplanes provide more vias and signaltraces without increasing in size, or in many instances, while actuallydecreasing in size. This has introduced significant difficulties indesigning and fabricating midplanes, as well as significant difficultiesin dealing with electrical noise and other electrical characteristics.Electrical noise is usually considered any undesirable electrical energyin an electronic system, including but not limited to, reflections,electromagnetic interference, mode conversions and unwanted coupling,such as cross-talk.

The trend for smaller, faster and more complex electronic systems hasalso required connectors to carry more and faster data signals in asmaller space without degrading the electrical characteristics of thesignal. Connectors can be made to carry more signals in less space byplacing signal conductors in a connector closer together. A majordifficulty with placing signal conductors closer together is thatelectrical noise between the signal conductors increases as the distancebetween signal conductors decreases and as the speed of the signalsincreases. In addition, as frequency content increases, there is agreater possibility of energy loss. Energy loss may be attributed toimpedance discontinuities, mode conversion, leakage from imperfectshielding, or undesired coupling to other conductors (crosstalk).Therefore, connectors are designed to control the mechanisms that enableenergy loss. Conductors composing transmission paths are designed tomatch system impedance, enforce a known propagating mode of energy,minimize eddy currents, and isolate alternate transmission paths fromone another. One example of controlling energy loss is the placement ofa conductor connected to a ground placed adjacent to a signal contactelement to determine an impedance and minimize energy loss in the formof radiation.

One way to control electrical noise in a connector is to utilizedifferential signals. Differential signals are signals represented by apair of signal conductors, called a “differential pair”. The voltagedifference between the pair of signal conductors represents the signal.If electrical noise is electromagnetically coupled to a differentialpair, the effect on each signal conductor of the pair should be similar.This renders a differential pair less sensitive to electrical noise ascompared with a single signal conductor. However, use of a differentialconnector, especially in a midplane system architecture, introducesfurther difficulties as vias corresponding to the differential pair oneither side of the midplane must each be electrically connected in themidplane and signal traces can only be routed between adjacentdifferential pairs.

What is desired, therefore, is to provide a midplane and a differentialconnector designed for such a midplane that addresses the difficultiesdescribed above.

SUMMARY OF THE INVENTION

In one embodiment of a midplane in accordance with the invention, themidplane has a first side to which contact ends of a first differentialconnector are connected and a second side opposite the first side towhich contact ends of a second differential connector are connected. Themidplane includes a plurality of vias extending from the first side tothe second side, with the vias providing first signal launches on thefirst side and second signal launches on the second side. The firstsignal launches are provided in a plurality of rows for electricallyconnecting to the contact ends of the first differential connector, witheach row having first signal launches along a first line and firstsignal launches along a second line substantially parallel to the firstline. The first signal launches along the first and second lines areoffset so that first signal launches along the first line and adjacentfirst signal launches along the second line correspond to differentialpairs of the first differential connector. The second signal launchesare provided in a plurality of columns for electrically connecting tothe contact ends of the second differential connector, with each columnhaving second signal launches along a third line and second signallaunches along a fourth line substantially parallel to the third line.The second signal launches along the third and fourth lines are offsetso that second signal launches along the third line and adjacent secondsignal launches along the fourth line correspond to differential pairsof the second differential connector.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a perspective view of an electronic system utilizing amidplane according to an embodiment of the present invention;

FIG. 2 is a partially exploded view of a differential electricalconnector assembly according to an embodiment of the present inventionthat may be used in the electronic system of FIG. 1;

FIG. 3 is a perspective view of a differential midplane connector shownin FIG. 2;

FIG. 4 is a perspective view showing rows of differential pair signalconductors and corresponding ground conductors of the differentialmidplane connector shown in FIG. 3 according to an embodiment of thepresent invention;

FIG. 4A is an alternative embodiment of FIG. 4, showing rows ofdifferential pair signal conductors and corresponding ground conductorsof the differential midplane connector shown in FIG. 3;

FIG. 5 is a bottom view showing first contact ends of the differentialpair signal conductors and corresponding ground conductors of thedifferential midplane connector shown in FIG. 4;

FIG. 6 is a perspective view of a differential daughtercard connectoraccording to an embodiment of the present invention shown in FIG. 2,with a wafer separated from the connector for clarity;

FIG. 7 is an exploded view of the wafer of FIG. 6 showing only thedifferential pair signal conductors and corresponding ground conductor;

FIG. 8A is a schematic top view of a portion of one side of the midplaneof FIG. 1, with a part of the surface removed to show a ground planelayer;

FIG. 8B is a schematic top view of a portion (the same portion as FIG.8A) of the other side of the midplane of FIG. 1, with a part of thesurface removed to show a ground plane layer;

FIG. 9A is a schematic view of a cross-section through the matingcontact region of a traditional differential midplane connector attachedto one side of a midplane;

FIG. 9B is a schematic view of a cross-section through the matingcontact region of a traditional differential midplane connector attachedto the other side of a midplane as illustrated in FIG. 9A;

FIGS. 9C and 9D are diagrams illustrating via hole patterns for FIGS. 9Aand 9B, respectively for traditional differential midplane connectors;

FIG. 10A is a schematic view of a cross-section through the matingcontact region of a differential midplane connector attached to one sideof a midplane according to an embodiment of the present invention;

FIG. 10B is a schematic view of a cross-section through the matingcontact region of a differential midplane connector attached to theother side of a midplane according to an embodiment of the presentinvention;

FIGS. 10C and 10D are diagrams illustrating via hole patterns for FIGS.10A and 10B, respectively for differential midplane connectors accordingto an embodiment of the present invention;

FIG. 11A is a perspective view of two differential electrical connectorassemblies attached to opposing sides of a midplane according to anembodiment of the present invention; and

FIG. 11B is a schematic side view of FIG. 11A, showing two pairs ofsignal conductors each mounted on opposing sides of a midplane andsharing common vias according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” “having,” “containing,”“involving,” and variations thereof herein, is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems.

Referring to FIG. 1, there is shown a sketch of an electronic system 100which utilizes a midplane 110 in accordance with the present invention.The midplane has a first side 112 and a second side 114. Daughtercards120A, 120B, 120C and 120D are electrically connected to the midplane 110on the second side 114. Daughtercards 130A, 130B and 130C areelectrically connected to the midplane 110 on the first side 112. Notethat the daughtercards 130A-130C on the first side 112 of the midplane110 are orthogonal in orientation to the daughtercards 120A- 120D on thesecond side 114 of the midplane 110. The concepts embodied in thepresent invention are especially applicable to such an orthogonalarchitecture electronic system.

While not shown in the sketch of FIG. 1, daughtercards 120A-120D and130A-130C are electrically connected to the midplane 110 by electricalconnector assemblies. FIG. 2 shows a preferred embodiment of such anelectrical connector assembly 200 in accordance with the presentinvention. Midplane 110 includes multiple signal traces that routesignals between daughtercards 120A-120D and 130A-130C of the electronicsystem 100. The midplane 110 is described in greater detail with respectto FIG. 7. It should be noted that the number of daughtercards 130A-130Cshown on the first side 112 and the number of daughtercards 120A-120Dshown on the second side 114 are for illustrative purposes only, and theactual number of daughtercards connected to the midplane 110 may varydepending upon the electronic system.

FIG. 2 shows the electrical connector assembly 200 that may be used toconnect the daughtercards 120A-120D and 130A-130C to the midplane 110 ofFIG. 1. The electrical connector assembly 200 is preferably adifferential electrical connector assembly. The electrical connectorassembly 200 includes a first differential electrical connector 300,which in the illustration connects to the midplane 110, and a seconddifferential electrical connector 400, which connects to one of thedaughtercards (daughtercard 120A is referenced for illustration in FIG.2). Typically, one or more second connectors 400 would be connected toeach daughtercard, with the corresponding number of first connectors 300connected to the midplane 110.

FIG. 3 shows a differential midplane connector 300 having a housing 302,which is preferably made of an insulative material. The housing 302 hassidewalls 304, 305, end walls 307, 308 and a base (not numbered).Disposed in the base of the housing 302 are a plurality of signalconductors 3 10 provided as differential pairs and a plurality of groundconductors 320, with each ground conductor 320 corresponding to adifferential pair of signal conductors 310 and positioned adjacentthereto. As shown in greater detail in FIGS. 4, 4A and 5, the signalconductors 310 and the ground conductors 320 are provided in a pluralityof rows. For exemplary purposes only, six rows 330a-330f are shown inFIG. 4, with each of the rows having six differential pairs of signalconductors 310 and six corresponding ground conductors 320. Note thatthe number of rows, the number of signal conductors 310 for each row,and the number of ground conductors 320 for each row may be any numberas desired. However, as will become more apparent in connection with thedescription of the midplane 110 in FIG. 8, it is preferable topre-select the number of rows, the number of signal conductors 310 foreach row, and the number of ground conductors 320 for each row to ensurea substantially square footprint for connecting to the midplane 110.

Each signal conductor 310 has a first contact end 312 connectable to themidplane 110, a second contact end 314, and an intermediate portion 316therebetween having a first width as measured from first edge 317 tosecond edge 318 of the signal conductor 310. Each ground conductor 320has a first contact end 322 connectable to the midplane 110, a secondcontact end 324, and an intermediate portion 326 therebetween having asecond width as measured from first edge 327 to second edge 328 of theground conductor 320. Preferably, the second width of the intermediateportion 326 of the ground conductor 320 is at least twice the firstwidth of the intermediate portion 316 of the signal conductor 310. Thisallows the ground conductor 320 to provide sufficient shielding to thecorresponding differential pair of signal conductors 310 from theelectromagnetic effects of signal conductors in adjacent rows.

In the preferred embodiment, the first contact end 322 of the groundconductor 320 includes a first contact arm 332 and a second contact arm333 spaced from the first contact arm 332. The first and second contactarms 332, 333 extend in the direction of the corresponding differentialpair of signal conductors 310. Preferably, the first and second contactarms 332, 333 extend beyond the plane of the corresponding signalconductors 310. This allows the contact arms 332, 333 to providesufficient shielding to the corresponding differential pair of signalconductors 310 from the electromagnetic effects of adjacent signalconductors in the row. Note that for each of the plurality of rows 330a-330 f, the first contact arm 332 of a ground conductor 320 is proximaland substantially parallel to the second contact arm 333 of an adjacentground conductor 320, except at an end of a row.

The drawings show that the first contact end 312 of each signalconductor 310 and the first contact end 322 of each ground conductor 320as press-fit contact tails. However, it should be apparent to one ofordinary skill in the art that the first contact ends 312, 322 may takeany known form, e.g., pressure-mount contacts, paste-in-hole solderattachment, contact tails adapted for soldering, etc., for connecting tothe midplane 110. In the preferred embodiment, the press-fit contacttails of the signal conductors 310 are oriented in a first direction andthe press-fit contact tails of the ground conductors 320 are oriented ina second direction substantially perpendicular to the first direction.

Referring to FIGS. 4 and 5, each differential pair of signal conductors310 of a row, e.g., row 330 a, has one first contact end 312(a) thatlies along a first line 350 and is parallel to the plurality of rows andan other first contact end 312(b) that lies along a second line 352 andis parallel to and spaced from the first line 350. The first contact end322 of the corresponding ground conductor 320 preferably lies along athird line 354 that is parallel to and spaced from the first and secondlines 350, 352. In the preferred embodiment, the third line 354 ispositioned between the first and second lines 350, 352. Thisconfiguration, as described in greater detail with respect to thedescription of the midplane 110 in FIG. 8, provides a substantiallysquare footprint for connecting to the midplane 110.

For each differential pair of signal conductors 310 of a row, the secondcontact ends 314 lie along a fourth line 356. The fourth line 356 ispreferably parallel to the plurality of rows. The second contact ends324 of the ground conductors 320 lie along a fifth line 358 that isparallel to and spaced from the fourth line 356.

Referring now to FIG. 4A, there is shown an alternative embodiment ofFIG. 4. In this embodiment, the signal conductors 310 are as shown inFIG. 4. However, instead of providing a ground conductor 320corresponding to each differential pair of signal conductors 310 asillustrated in FIG. 4, there is provided a single first ground conductor370 for each row of signal conductors 310. The first ground conductor370 extends substantially the length of the corresponding row, where therows are referenced by 330 a′-330 f′ in FIG. 4A. Each first groundconductor 370 has a plurality of mating contact ends 374 that areconnectable to the corresponding ground conductor of the seconddifferential electrical connector 400. The number of mating contact ends374 of each first ground conductor 370 is preferably the same as thenumber of differential pairs of signal conductors 310 of eachcorresponding row. In the example illustrated in FIG. 4A, there are sixmating contact ends 374 corresponding to the six differential pairs ofsignal conductors 310.

A plurality of second ground conductors 380 are also provided, with eachsecond ground conductor 380 electrically connected to each first groundconductor 370 and oriented substantially perpendicular to the firstground conductors 370. Each second ground conductor 380 extendssubstantially the length of the plurality of rows 330 a′-330 f′, andeach second ground conductor 380 is positioned between adjacentdifferential pairs of signal conductors 310 of each row 330 a′-330 f′.The second ground conductors 380 are each provided with a first contactend connectable to the midplane 110. Preferably, the first contact endof each second ground conductor 380 includes a plurality of contact pins382 that are oriented perpendicularly to the orientation of the contactpins 312 of the signal conductors 310. Note that for each row 330 a′-330f′, there is a contact pin 382 of a second ground conductor 380 adjacenteach differential pair of signal conductors 310. And for each row 330a′-330 f′, the contact pins 382 for the row lie along a third line 354,as described with respect to FIG. 5. Other suitable configurations ofsignal conductors 310 and ground conductors 320 may also be used, aswill be apparent to those of ordinary skill in the art.

Referring now to FIGS. 6 and 7, there is shown the second differentialelectrical connector 400 of the electrical connector assembly 200 whichmates to the first differential electrical connector 300 on one side andelectrically connects to one of the daughtercards (e.g., daughtercard130C) on another side. The second differential electrical connector 400includes a plurality of wafers 401, where each of the plurality ofwafers 401 corresponds to one of the plurality of rows (e.g., 330 a-330f of FIG. 4) of the first differential electrical connector 300. Thus,the number of wafers 401 of the second differential electrical connector400 is the same as the number of rows of the first differentialelectrical connector 300. Each wafer 401 includes a housing 402, whichis preferably made of an insulative material. A plurality of signalconductors 410 provided as differential pairs are held in the housing402 with a corresponding ground conductor 420 positioned adjacentthereto. The signal conductors 410 and the corresponding groundconductor 420 are shown in greater detail in FIG. 7. Note that thenumber of differential pairs of signal conductors 310 provided in a rowof the first differential electrical connector 300 is the same as thenumber of differential pairs of signal conductors 410 provided in thecorresponding wafer 401 of the second differential electrical connector400.

Each signal conductor 410 has a first contact end 412 connectable to oneof the daughtercards (e.g., 120A-120D, 130A-130C of FIG. 1), a secondcontact end 414 connectable to the second contact end 314 of acorresponding signal conductor 310 of the first differential electricalconnector 300, and an intermediate portion 416 therebetween. Each groundconductor 420 has a first contact end 422 connectable to thedaughtercard, a second contact end 424 connectable to the second contactends 324 of the corresponding ground conductors 320 of the firstdifferential electrical connector 300, and an intermediate portion 426therebetween. The drawings show the first contact end 412 of each signalconductor 410 and the first contact end 422 of the ground conductor 420as press-fit contact tails. However, it should be apparent to one ofordinary skill in the art that the first contact ends 412, 422 may takeany form, e.g., pressure-mount contacts, paste-in-hole solderattachment, contact tails adapted for soldering, etc., for connecting tothe daughtercard.

In the preferred embodiment, the ground conductor 420 is a ground shieldthat provides electrical shielding to the corresponding signalconductors 410 of the wafer 401. However, a plurality of groundconductors may be utilized instead of a single ground shield, as knownin the art. Provided in the second contact end 424 of the ground shield420 are slits 430. Preferably, the slits 430 are positioned betweenadjacent differential pairs of signal conductors 410.

Each of the slits 430 is configured to receive and electrically connectto a ground conductor 440 that is oriented perpendicular to the groundconductor 420 of the wafer 401. Note that the ground conductor 440 ispreferably configured as a ground strip, as shown in FIG. 6. Each groundstrip 440 electrically connects to each ground conductor 420 of thewafers 401. In this manner, the ground strips 440 electrically separateadjacent second contact ends 414 of differential pairs of signalconductors 410. The grid-like shielding pattern formed by the groundshields 420 and the ground strips 440 provides effective electricalshielding (e.g., from electrical noise) for the differential pairs ofsignal conductors 410. This grid-like shielding pattern formed by theground shields 420 and the ground strips 440 is housed in a shroud 450,which is preferably insulative.

Referring now to FIG. 8A, there is shown a top view of a portion of thefirst side 112 of the midplane 110 of FIG. 1, with a part of the surfaceremoved to reveal a ground plane layer 150. FIG. 8B shows a top view ofthe portion (same portion as in FIG. 8A and viewed from the sameperspective as FIG. 8A) of the second side 114 of the midplane 110 ofFIG. 1, with a part of the surface removed to reveal a ground planelayer 170. The portion of the midplane 110 shown in FIGS. 8A and 8Bcorrespond to the footprint of a differential electrical connector, suchas the differential electrical connector 300, that connects to themidplane 110. Note that the portion of the first side 112 of themidplane 110 shown in FIG. 8A provides a similar interface for adifferential electrical connector as the portion of the second side 114of the midplane 110 shown in FIG. 8B.

As known in the art, a midplane is generally a multi-layer printedcircuit board formed of multiple layers of dielectric substrates withsignal traces or planes formed on one or more of the dielectric layers.Further, the multi-layer printed circuit board will typically have aground plane formed on one or more of the dielectric layers. Viasgenerally extend between layers of a multi-layer printed circuit board.Vias which extend through all layers of a multi-layer printed circuitboard are sometimes referred to as through-holes. The vias are usuallyformed after the layers of substrates are formed into a printed circuitboard. Conductive vias generally intersect signal traces on differentlayers. Conductive vias also interconnect components mounted on theprinted circuit board to signal traces on inner layers of the printedcircuit board.

FIG. 8A shows the ground plane 150, which is formed on one of thedielectric layers of the midplane 110. FIG. 8B shows the ground plane170, which is formed on one of the dielectric layers of the midplane110. Typically, the midplane 110 will have more than one ground plane,and ground planes 150, 170 will be different ground planes. However, theground planes 150, 170 may be the same ground plane without departingfrom the scope of the present invention. The midplane 110 has aplurality of vias 152, 154 extending from the first side 112 to thesecond side 114. Thus, vias 152, 154 are through-hole vias. The vias 152are signal connecting conductive vias and the vias 154 are groundconnecting conductive vias. Note that the signal connecting conductivevias 152 on the first side 112 of the midplane 110 provide first signallaunches 155 for differential pairs of the differential connectorconnected to the first side 112 and the signal connecting conductivevias 152 on the second side 114 of the midplane 110 provide secondsignal launches 175 for differential pairs of the differential connectorconnected to the second side 114. The ground connecting conductive vias154 on the first side 112 of the midplane 110 provide first groundlaunches 157 for differential pairs of the differential connectorconnected to the first side 112 and the ground connecting conductivevias 154 on the second side 114 of the midplane 110 provide secondground launches 177 for differential pairs of the differential connectorconnected to the second side 114.

The first signal launches 155 are provided in a plurality of rows 156a-156 f, as shown in FIG. 8A, for electrically connecting to adifferential connector. In the example of FIG. 8A, the six rows 156a-156 f shown correspond to the six rows 330 a-330 f of differentialpairs of signal conductors 310 of the first differential electricalconnector 300 shown in FIGS. 4 and 5. Each signal connecting conductivevia 152 of a pair corresponding to a differential pair of signalconductors is electrically isolated from the other signal connectingconductive via 152 of the pair. Further, for each pair of signalconnecting conductive vias 152 corresponding to a differential pair ofsignal conductors, there is an area 158 surrounding the pair of signalconnecting conductive vias 152 that is free of the ground plane 150.This free area 158 is sometimes referred to as an “antipad.” It has beenfound that by ensuring that the area surrounding the pair of signalconnecting conductive vias 152 is free of the ground plane 150 (while aregion between adjacent pairs of signal connecting conductive vias 152includes the ground plane 150), there is significantly improved signalperformance. Note that while the preferred embodiment of the inventionillustrates a substantially oval antipad 158, the antipad 158 may takeother shapes. See, e.g., U.S. Pat. No. 6,607,402, incorporated byreference herein. For example, the antipad 158 may be substantiallyrectangular in shape or may be substantially figure-8 in shape.

As with the first contact ends 312 of each differential pair of signalconductors 310 of the first differential electrical connector 300 (FIGS.4 and 5), one signal connecting conductive via 152 of a pair lies alonga first line 160 and the other signal connecting conductive via 152 ofthe pair lies along a second line 162 that is parallel to and spacedfrom the first line 160. Also, as with the first contact ends 312 ofeach differential pair of signal conductors 310 of the firstdifferential electrical connector 300, the signal connecting conductivevias 152 of a pair are offset. Preferably, the signal connectingconductive vias 152 of a pair are offset substantially at a forty-five(45) degree angle relative to the orientation of the rows 156 a-156 f.Note that because of this offset of the signal connecting conductivevias 152 of a pair, the antipad 158 surrounding the pair is alsopreferably oriented substantially at a forty-five (45) degree anglerelative to the orientation of the rows 156 a-156 f.

The first ground launches 157 are also provided in the plurality of rows156 a-156 f, as shown in FIG. 8A, for electrically connecting to adifferential connector. For each of the rows 156 a-156 f, the firstground launches 157 are provided along a line 164 that is adjacent toand substantially parallel to the first and second lines 160, 162.Preferably, this line 164 is spaced between the first and second lines160, 162. Further, for each of the rows 156 a-156 f, the number of firstground launches 157 is preferably greater than the number of pairs offirst signal launches 155. In the example of FIG. 8A, the number offirst ground launches 157 of a row 156 a-156 f is seven (7), while thenumber of pairs of first signal launches 155 of a row 156 a-156 f is six(6).

Referring now to FIG. 8B, there is shown the second signal launches 175that are provided in a plurality of columns 176 a-176 f for electricallyconnecting to a differential connector. In the exemplary illustration ofFIG. 8B, the six columns 176 a-176 f shown correspond to the six rows330 a-330 f of differential pairs of signal conductors 310 of the firstdifferential electrical connector 300 shown in FIGS. 4 and 5. Thesecolumns 176 a-176 f are orthogonal to the rows 156 a-156 f of FIG. 8A.This orthogonality of the rows 156 a-156 f on the first side 112 of themidplane 110 relative to the columns 176 a-176 f on the second side 114of the midplane 100 corresponds to and accommodates the orthogonality ofthe daughtercards 130A-130C on the first side 112 relative to thedaughtercards 120A-120D on the second side 114 (see FIG. 1).

Same as in FIG. 8A, each signal connecting conductive via 152 of a paircorresponding to a differential pair of signal conductors iselectrically isolated from the other signal connecting conductive via152 of the pair. In fact, the through-hole signal connecting conductivevias 152 shown in FIG. 8A are the same through-hole signal connectingconductive vias 152 shown in FIG. 8B. Thus, for the portion of themidplane 110 shown in FIGS. 8A and 8B, the number of first signallaunches 155 equals the number of second signal launches 175. Note thatby designing a differential electrical connector that provides asubstantially square footprint for connecting to the midplane 110 (suchas the first differential electrical connector 300), it is possible toprovide the midplane 10 that utilizes the same through-hole signalconnecting conductive vias 152 for connecting a differential electricalconnector to the first side 112 and a differential electrical connectorto the second side 114. In this manner, the midplane design of thepresent invention (i) significantly reduces the required layers and sizeof the midplane, (ii) provides for an easier to design and manufacturemidplane, (iii) improves the signal characteristics of the transmittedsignals, and (iv) significantly reduces the materials and cost of themanufactured midplane.

For each pair of signal connecting conductive vias 152 corresponding toa differential pair of signal conductors, there is an area 178surrounding the pair of signal connecting conductive vias 152 that isfree of the ground plane 170. This antipad 178 is similar to the antipad158 of FIG. 8A. It has been found that by ensuring that the areasurrounding the pair of signal connecting conductive vias 152 is free ofthe ground plane 170 (while a region between adjacent pairs of signalconnecting conductive vias 152 includes the ground plane 170), there issignificantly improved signal performance. Note that while the preferredembodiment of the invention illustrates a substantially oval antipad178, the antipad 178 may take other shapes. For example, the antipad 178may be substantially rectangular in shape or may be substantiallyfigure-8 in shape.

As with the first contact ends 312 of each differential pair of signalconductors 310 of the first differential electrical connector 300 (FIGS.4 and 5), one signal connecting conductive via 152 of a pair lies alonga third line 180 and the other signal connecting conductive via 152 ofthe pair lies along a fourth line 182 that is parallel to and spacedfrom the third line 180. Also, as with the first contact ends 312 ofeach differential pair of signal conductors 310 of the firstdifferential electrical connector 300, the signal connecting conductivevias 152 of a pair are offset. Preferably, the signal connectingconductive vias 152 of a pair are offset substantially at a forty-five(45) degree angle relative to the orientation of the columns 176 a-176f. Note that because of this offset of the signal connecting conductivevias 152 of a pair, the antipad 178 surrounding the pair is alsopreferably oriented substantially at a forty-five (45) degree anglerelative to the orientation of the columns 176 a-176 f.

The second ground launches 177 are also provided in the plurality ofcolumns 176 a-176 f, as shown in FIG. 8B, for electrically connecting toa differential connector. For each of the columns 176 a-176 f, thesecond ground launches 177 are provided along a line 184 that isadjacent to and substantially parallel to the third and fourth lines180, 182. Preferably, this line 184 is spaced between the third andfourth lines 180, 182. As described above, the columns 176 a-176 f ofthe second side 114 are orthogonal to the rows 156 a-156 f of the firstside 112. Thus, the third and fourth lines 180, 182 are orthogonal tothe first and second lines 160, 162 of FIG. 8A. For each of the columns176 a-176 f, the number of second ground launches 177 is preferablygreater than the number of pairs of second signal launches 175. In theexample of FIG. 8B, the number of second ground launches 177 of a column176 a-176 f is seven (7), while the number of pairs of second signallaunches 175 of a column 176 a-176 f is six (6).

FIGS. 9A through 9D and FIGS. 10A through 10D illustrate the advantageof offset contact tails associated with the differential midplaneconnector 300 according to an embodiment the present invention. FIG. 9Aillustrates a cross section through a traditional connector near thesecond contact end region. FIG. 9A shows that connector 300 has apair-wise orientation. As used herein, “pair-wise” orientation indicatesthat the connector is designed with pairs of signal conductors adaptedto preferentially electrically couple to each other. For example, thedirection of the displacement between one conductor of a pair near thefirst contact end, e.g., 312(a), and the second conductor of the pairnear the first contact end, e.g., 312(b), provides the orientation ofthe pair.

Multiple design techniques may be used to create a pair-wise orientationof a connector. These design techniques may be used alone or incombination. In the illustrated embodiment, shields are used to createpreferential coupling between pairs. A pair-wise orientation is createdbecause the signal conductors of each pairs are oriented in theconnector with the signal conductors of a pair displaced from each otherin a direction parallel to the shielding.

As another example of a technique to create a pair-wise orientation, thesignal conductors of a pair may be routed closer to each other than tothe next nearest signal conductor.

A pair-wise orientation is desirable for a differential connectorbecause it increases the coupling between the conductors that form apair and decreases coupling to signal conductors that form an adjacentpair. As a result, each differential signal path is less susceptible toextraneous electromagnetic fields that could induce noise. Further, thecoupling between adjacent pairs is reduced, thereby reducing cross-talkwithin the connector, allowing the connector to operate with greatersignal integrity. With greater signal integrity, more signals may berouted through the connector or signals of higher frequency may passthrough the connector.

In FIG. 9A, second contact ends 314A and 314B forming a differentialpair are aligned along column 910A. Such an alignment is similar to aconnector 300 mounted on surface 112 to receive a connector on board130A, such as shown in FIG. 1, with column 910A being aligned along anaxis (shown here in the z axis) that is parallel to rows 330 a-330 f.

FIG. 9C shows a via hole pattern needed to receive first contact endsfrom signal conductors in a traditional connector mounted as shown inFIG. 9A if offset first contact ends are not used. FIG. 9C shows thehole pattern having the same alignment along an axis as the signalconductors for the connector in FIG. 9A, shown here in the z axis.

FIG. 9B shows a cross section of a connector with the second contactends of a differential pair aligned along row 920A. Such an alignment issimilar to a connector 300 mounted on surface 114 to receive a connectoron board 120A, such as shown in FIG. 1, with row 920A being alignedalong an axis (shown here in the x axis) that is parallel to rows 330a-330 f. Because board 120A is perpendicular to board 130A, thepair-wise orientation and the alignment of the connector in FIG. 9B isorthogonal to the pair-wise orientation and the alignment of theconnector in FIG. 9A.

FIG. 9D shows a via hole pattern needed to receive first contact endsfrom signal conductors in a traditional connector mounted as shown inFIG. 9B if offset first contact ends are not used. FIG. 9D shows thehole pattern having the same alignment along an axis as the signalconductors for the connector in FIG. 9B, shown here in the x axis.

When the via hole patterns of FIGS. 9C and 9D are formed on oppositesides of a midplane, no amount of shifting of the hole pattern allowsboth holes for the same pair to be aligned. For example, if holes 930Aand 940A are aligned, holes 930B and 940B cannot align. To connect asignal pair on one side of a midplane to another using a traditionalconnector design, routing traces within the midplane are required tomake connections between the vias in which the connectors on oppositesides of the midplane are mounted.

FIGS. 10A through 10D illustrates an advantage that can be obtained withoffset contact tails, 312(a), 312(b) according to an embodiment of thepresent invention. FIGS. 10A and 10B show the second contact ends 314A,314B and 324A aligned along the same axes (shown here in the z and xaxes, respectively) as previously shown in FIGS. 9A and 9B. With aforty-five (45) degree offset associated with the orientation of thecontact tails 312(a), 312(b) from the second contact end position, thereis a corresponding forty-five (45) degree offset for hole patternsassociated with each differential pair. Thus, FIGS. 10C and 10D show viahole patterns needed to receive first contact ends 312(a) and 312(b)from signal conductors 310 as mounted in FIGS. 10A and 10B,respectively. FIG. 10C shows the hole pattern having an alignment alongan axis z′ that has an angle about forty-five degrees from the alignment(shown here in the z axis) of the second contact ends, 314 as shown inFIG. 10A. Similarly, FIG. 10D shows the hole pattern having an alignmentalong an axis x′ that has an angle about forty-five degrees from thealignment (shown here in the x axis) of the second contact ends, 314 asshown in FIG. 10B. As a result, even though the mating contact portions314 of connectors 300 on opposing sides of midplane 110 have orthogonalpair-wise orientations and alignments, the holes for differential pairson opposing sides of midplane 110 have the same pattern and may bealigned. If the hole patterns on opposite sides of the midplane align,connectors in opposite sides of the midplane may be inserted into thesame vias.

This alignment is shown in FIG. 11A, which shows connectors 300A and300B mounted on opposite sides of midplane 110. Connector 300A mateswith connector 400A. Connector 300B mates with connector 400B. Becauseconnectors 400A and 400B are attached to printed circuit boards that aremounted with different orientations, the pair-wise orientation ofconnectors 400A and 400B have different orientations. In the illustratedembodiment, connectors 400A and 400B are mounted orthogonal to eachother. To mate with connectors 400A and 400B, connectors 300A and 300Bmust similarly be mounted orthogonal to each other. Consequently,connector 300A has a pair-wise orientation and alignment and connector300B has a pair-wise orientation and alignment.

Despite the different pair-wise orientations of connectors 300A and300B, the offset pattern of contact tails 312 allows the contact tails312 of connectors 300A and 300B to be mounted using one set of viaholes. Further, every pair of signal conductors in connector 300A may bemounted in the same two vias as a pair of signal conductors in connector300B.

FIG. 11B is a side view of a pair of signal conductors within connectors300A and 300B mounted on opposing sides of a midplane 110. The signalconductors have an orientation and alignment on one side of the boardand an orientation and alignment on the opposing side. Despiteorthogonal orientations, the offset of the contact tails of both pairsallows the contact tails to align so that they may be connected throughvias 1110 a and 1110 b, respectively.

In this way, the two signals that form one differential signal arerouted together from a daughter card on one side of midplane 110,through a first set of connectors to midplane 110, through midplane 110to a second set of connectors to a second daughter card. The two signalconductors are kept together as a pair, thereby providing desirablesignal integrity properties. Further, the transmission path may beoptimized for carrying differential signals. As described above, eachconnector may be constructed with shielding, signal conductorpositioning or other structures that provide a pair-wise orientationthat increases the signal integrity when carrying differential signals.

In the midplane, connections between the signal conductors on opposingsides of the midplane may be made using only the vias of the midplane tocarry the signal. No traces within the midplane are needed to carrydifferential signals from one side of the midplane to another.Eliminating traces, and transitions between vias and traces, within themidplane means less distortion of the signal occurs in the midplane,further increasing the signal integrity of the connector. Further, FIGS.8A and 8B illustrate that ground clearances around differential pairsmay be structured to further improve the integrity of signals passingthrough the midplane oriented as differential pairs.

A number of preferred and alternative embodiments of the invention havebeen described. Nevertheless, it will be apparent to one of ordinaryskill in the art that various modifications and alterations of thisinvention may be made without departing from the scope and spirit ofthis invention. Accordingly, other embodiments are within the scope ofthe appending claims.

1. A differential electrical connector having differential pairs held inan insulative housing in a plurality of rows, wherein each of theplurality of rows comprises: a plurality of signal conductors providedas differential pairs, with each signal conductor having a first contactend connectable to a printed circuit board, a second contact end, and anintermediate portion therebetween having a first width; for eachdifferential pair of signal conductors, one first contact end lies alonga first line that is parallel to the plurality of rows and the otherfirst contact end lies along a second line that is parallel to andspaced from the first line; a plurality of ground conductors with eachground conductor corresponding to a differential pair of signalconductors; each ground conductor having a first contact end connectableto the printed circuit board, a second contact end, and an intermediateportion therebetween having a second width that is at least twice thefirst width; and the first contact end of each ground conductor lyingalong a third line that is parallel to and spaced from the first andsecond lines.
 2. The differential electrical connector of claim 1,wherein the first contact end of each ground conductor further comprisesa first contact arm and a second contact arm spaced from the firstcontact arm, the first and second contact arms extending in thedirection of the corresponding differential pair of signal conductors.3. The differential electrical connector of claim 2, wherein for each ofthe plurality of rows, the first contact arm of a ground conductor isproximal and parallel to the second contact arm of the adjacent groundconductor.
 4. The differential electrical connector of claim 2, whereinthe first contact end of each signal conductor comprises a contact pinoriented in a first direction and each of the first and second contactarms of each ground conductor further comprises a contact pin orientedin a second direction substantially perpendicular to the firstdirection.
 5. The differential electrical connector of claim 1, whereinthe third line is positioned between the first and second lines.
 6. Thedifferential electrical connector of claim 1, wherein for each of theplurality of rows, the second contact ends of the signal conductors liealong a fourth line and the second contact ends of the ground conductorslie along a fifth line parallel to and spaced from the fourth line. 7.The differential electrical connector of claim 1, wherein the number ofrows, the number of signal conductors for each of the rows, and thenumber of ground conductors for each of the rows are pre-selected toensure that the first contact ends of the signal conductors and theground conductors form a substantially square footprint for connectingto the printed circuit board.
 8. A differential electrical connectorassembly, which comprises: a first differential electrical connectorhaving differential pairs held in a first insulative housing in aplurality of rows, wherein each of the plurality of rows includes: aplurality of first signal conductors provided as differential pairs,with each first signal conductor having a first contact end connectableto a first printed circuit board, a second contact end, and anintermediate portion therebetween; for each differential pair of firstsignal conductors, one first contact end lies along a first line that isparallel to the plurality of rows and the other first contact end liesalong a second line that is parallel to and spaced from the first line;a plurality of first ground conductors with each first ground conductorcorresponding to a differential pair of first signal conductors; eachfirst ground conductor having a first contact end connectable to thefirst printed circuit board, a second contact end, and an intermediateportion therebetween; the first contact end of each first groundconductor lying along a third line that is parallel to and spaced fromthe first and second lines; a second differential electrical connectorhaving differential pairs provided in a plurality of wafers, whereineach of the plurality of wafers corresponds to one of the plurality ofrows of the first differential electrical connector and includes: asecond insulative housing; a plurality of second signal conductorsprovided as differential pairs and held in the second insulativehousing, with each second signal conductor having a first contact endconnectable to a second printed circuit board, a second contact endconnectable to the second contact end of a corresponding first signalconductor, and an intermediate portion therebetween; a second groundconductor having a first contact end connectable to the second printedcircuit board, a second contact end connectable to the second contactend of a corresponding first ground conductor, and an intermediateportion therebetween; and wherein the second differential electricalconnector further includes a third ground conductor electricallyconnected to the second ground conductor of each wafer, the third groundconductor oriented substantially perpendicular to the second groundconductor of each wafer.
 9. The differential electrical connectorassembly of claim 8, wherein for the first differential electricalconnector, the intermediate portion of each first signal conductor has afirst width and the intermediate portion of each first ground conductorhas a second width that is at least twice the first width.
 10. Thedifferential electrical connector assembly of claim 8, wherein for thefirst differential electrical connector, the first contact end of eachfirst ground conductor further comprises a first contact arm and asecond contact arm spaced from the first contact arm, the first andsecond contact arms extending in the direction of the correspondingdifferential pair of first signal conductors.
 11. The differentialelectrical connector assembly of claim 10, wherein for the firstdifferential electrical connector, the first contact end of each firstsignal conductor comprises a contact pin oriented in a first directionand each of the first and second contact arms of each first groundconductor further comprises a contact pin oriented in a second directionsubstantially perpendicular to the first direction.
 12. The differentialelectrical connector assembly of claim 8, wherein for the firstdifferential electrical connector, the number of rows, the number offirst signal conductors for each of the rows, and the number of firstground conductors for each of the rows are pre-selected to ensure thatthe first contact ends of the first signal conductors and the firstground conductors form a substantially square footprint for connectingto the first printed circuit board.
 13. The differential electricalconnector assembly of claim 8, wherein for the second differentialelectrical connector, the second ground conductor comprises a groundshield that provides electrical shielding to the second signalconductors of the corresponding wafer, and the third ground conductorcomprises a plurality of ground strips, with each ground stripelectrically contacting the ground shield of each wafer.
 14. Thedifferential electrical connector assembly of claim 13, wherein for thesecond differential electrical connector, the plurality of ground stripselectrically separate adjacent second contact ends of differential pairsof second signal conductors such that the second contact ends of eachdifferential pair of second signal conductors are electrically shieldedby ground shields and ground strips.
 15. A differential electricalinterconnection system, which comprises: a first differential electricalconnector having differential pairs held in a first insulative housingin a plurality of rows, wherein each of the plurality of rows includes:a plurality of first signal conductors provided as differential pairs,with each first signal conductor having a first contact end connectableto a first side of a midplane circuit board, a second contact end, andan intermediate portion therebetween; for each differential pair offirst signal conductors, one first contact end lies along a first linethat is parallel to the plurality of rows and the other first contactend lies along a second line that is parallel to and spaced from thefirst line; a plurality of first ground conductors with each firstground conductor corresponding to a differential pair of first signalconductors; each first ground conductor having a first contact endconnectable to the first side of the midplane circuit board, a secondcontact end, and an intermediate portion therebetween; wherein for thefirst differential electrical connector, the number of rows, the numberof first signal conductors for each of the rows, and the number of firstground conductors for each of the rows are pre-selected to ensure thatthe first contact ends of the first signal conductors and the firstground conductors form a substantially square footprint for connectingto the first side of the midplane circuit board; a second differentialelectrical connector having differential pairs held in a secondinsulative housing in a plurality of columns, wherein the columns areoriented perpendicular to the rows of the first differential electricalconnector and each of the plurality of columns includes: a plurality ofsecond signal conductors provided as differential pairs, with eachsecond signal conductor having a first contact end connectable to asecond side of the midplane circuit board, a second contact end, and anintermediate portion therebetween; for each differential pair of secondsignal conductors, one first contact end lies along a third line that isparallel to the plurality of columns and the other first contact endlies along a fourth line that is parallel to and spaced from the thirdline; a plurality of second ground conductors with each second groundconductor corresponding to a differential pair of second signalconductors; each second ground conductor having a first contact endconnectable to the second side of the midplane circuit board, a secondcontact end, and an intermediate portion therebetween; wherein for thesecond differential electrical connector, the number of columns, thenumber of second signal conductors for each of the columns, and thenumber of second ground conductors for each of the columns arepre-selected to ensure that the first contact ends of the second signalconductors and the second ground conductors form a substantially squarefootprint for connecting to the second side of the midplane circuitboard; and the midplane circuit board includes a plurality of viasextending from the first side to the second side with the vias providingfirst signal launches on the first side for electrically connecting tothe first contact ends of the first signal conductors and the firstground conductors and the vias providing second signal launches on thesecond side for electrically connecting to the first contact ends of thesecond signal conductors and the second ground conductors.
 16. Thedifferential electrical interconnection system of claim 15, wherein thefirst contact ends of the first ground conductors and the second groundconductors further comprise a first contact arm and a second contact armspaced from the first contact arm.
 17. A differential electricalconnector having differential pairs held in a housing in a plurality ofrows, wherein the differential electrical connector comprises: each ofthe plurality of rows including: a plurality of signal conductorsprovided as differential pairs, with each signal conductor having afirst contact end connectable to a printed circuit board; for eachdifferential pair of signal conductors, one first contact end lies alonga first line that is parallel to the plurality of rows and the otherfirst contact end lies along a second line that is parallel to andspaced from the first line; a first ground conductor corresponding tothe plurality of signal conductors of the row, the first groundconductor extending substantially the length of the row; a plurality ofsecond ground conductors, with each second ground conductor electricallyconnected to the first ground conductor of each row and orientedsubstantially perpendicular to the first ground conductor of each row;each second ground conductor extending substantially the length of theplurality of rows; and each second ground conductor positioned betweenadjacent differential pairs of each row and each second ground conductorhaving a first contact end connectable to the printed circuit board. 18.The differential electrical connector of claim 17, wherein the firstcontact end of each signal conductor comprises a contact pin oriented ina first direction and the first contact end of each second groundconductor comprises a plurality of contact pins oriented in a seconddirection substantially perpendicular to the first direction.
 19. Thedifferential electrical connector of claim 18, wherein for each row,there are contact pins of the second ground conductors adjacent eachdifferential pair of signal conductors.
 20. The differential electricalconnector of claim 19, wherein for each row, the contact pins of thesecond ground conductors lie along a third line that is parallel to andspaced from the first and second lines.